The field of the present invention is screen separators using vibratory motion to enhance separation.
Separation, sifting and the like through screens have long been accomplished with the assistance of vibratory motion. Such motion has been used as a means for vibrating the screens through which material is to pass, thereby using inertia and particle interaction of the material itself in assisting it through the screen, reducing screen blinding effects and physically breaking up clumps of material to improve screening efficiency. Such vibration also can be used as a means for advancing material along a surface. In screening, advancement and screening are both enhanced by vibratory motion. One such screen device is disclosed in U.S. Pat. No. 5,265,730, the disclosure of which is incorporated herein by reference. Another is disclosed in U.S. Pat. No. 4,582,597, the disclosure of which is incorporated herein by reference. Also in screening, vibratory motion can be used to cause impacts by the screen with solid elements positioned adjacent the screen for additional cleaning efforts. Reference may be made to U.S. Pat. No. 5,051,171, the disclosure of which is incorporated herein by reference.
A plurality of motions have been commonly used for the screening of materials. Round motion may be generated by a simple eccentric weight located roughly at the center of gravity of a resiliently mounted screening device with the rotational axis extending perpendicular to the vertical symmetrical plane of the separator. Such motion is considered to be excellent for particle separation and excellent for screen life. It requires a very simple mechanism, a single rotationally driven eccentric weight. However, round motion acts as a very poor conveyor of material and becomes disadvantageous in continuous feed systems where the oversized material is to be continuously removed from the screen surface. Machines are also known with two parallel axes of eccentric rotation extending perpendicular to the symmetrical plane.
Another common motion is achieved through the counter rotation of adjacent eccentric vibrators also affixed to a resiliently mounted screening structure. Through the orientation of the eccentric vibrators at an angle to the screening plane, linear vibration may be achieved at an angle to the screen plane. Such inclined linear motion has been found to be excellent for purposes of conveying material across the screen surface. However, it has been found to be relatively poor for purposes of separation and is very hard on the screens.
Another motion commonly known as multi-direction elliptical motion is induced where a single rotary eccentric vibrator is located at a distance from the center of gravity of the screening device. This generates elliptical motions in the screening device. However, the elliptical motion of any element of the screen has a long axis passing through the axis of the rotary eccentric vibrator. Thus, the motion varies across the screening plane in terms of direction. This motion has been found to produce efficient separation with good screen life. As only one eccentric is employed, the motion is simple to generate. However, such motion is very poor as a conveyor.
Another motion similar to the counter rotation of adjacent eccentric vibrators is illustrated in U.S. Pat. No. 5,265,730. Uni-directional elliptical motion is generated through the placement of two rotary eccentric vibrators with the axes of the vibrators similarly inclined from the vertical away from the direction of material travel and oppositely inclined from the vertical in a plane perpendicular to the direction of material travel. The inclination of the large axis of the elliptical motion relative to the screen surface is controlled by the inclination of the rotary eccentric vibrators away from the intended direction of travel of the material on the screen surface. The inclination of the vibrators in a plane perpendicular to the intended direction of material travel varies the width of the ellipse. These devices have been found to require substantial frame structures to accommodate the opposed forces imposed upon the frame.
In reviewing the motions typically associated with rectangular screening devices, compromises are inevitable. One typically must choose among strengths and weaknesses in conveying capability, screening capability and screen life.
The present invention is directed to a vibratory screen separator having a versatile vibration generating system which does not place large opposed forces on the overall frame structure.
In a first separate aspect of the present invention, a resiliently mounted frame rotationally mounts two eccentric weight systems. These eccentric weight systems include axes of eccentric force which are coincident with one another. Each of the weight systems is symmetrical about a center plane of the resiliently mounted frame, that center plane being parallel to the direction of material travel and normal to the plane of the screen mounting on the resiliently mounted frame. A drive system rotates the eccentric weights of the systems to effect coincident axes.
In a second separate aspect of the present invention, the device of the first aspect may assume a particularly preferred configuration with the eccentricities of the systems being unequal and the ratio of the speeds between systems being constant. With coincident effective axes, the eccentric weight systems may be located at the center of gravity of the frame.
In a third separate aspect of the present invention, a vibratory screen separator includes a resiliently mounted frame to which two eccentric weights are rotationally mounted about coincident axes. The weights are driven in opposite directions and are each symmetrical about the center plane identified in the first aspect.
In a fourth separate aspect of the present invention, any of the foregoing aspects may further include particular features such as coincident effective axes of eccentric force, operation at the center of gravity of the frame, variations in eccentricity between eccentrics and phase orientation of the eccentric weights to define and orient elliptical motion. Drive systems capable of phase adjustment are also contemplated.
In a fifth separate aspect of the present invention, various combinations of the foregoing aspects are contemplated to provide system advantage.
Accordingly, it is an object of the present invention to provide improved vibratory screen separator motion. Other and further objects and advantages will appear hereinafter.